1. Field of the Invention
The present invention relates to a monolithic spider for an epicyclic reduction unit.
2. Background Information
Epicyclic or sun-and-planet reduction units are known in which reduction of the rpm rate between the input or driving shaft and the output or driven shaft is achieved by a gear system having a plurality of reduction stages, each of which is substantially composed of a central pinion meshing with a set of three planetary gears that are rotatably supported on respective pivots cantilevered out from a flange. The flange and its associated assembly is known as a spider.
The planetary gears are supported on the pivots by smooth or rolling bearings. The bearings are composed of two concentric rings which form the tracks for the travel of the rolling bodies (rollers or balls) of the bearings. In the case of rolling bearings, designs have increased the load-bearing capacity of the pivots and therefore their resistance to the mechanical stresses that occur during operating conditions without increasing the external dimensions of the bearings. Specifically, it has been known to eliminate the internal contrast ring of the bearing and to provide a suitable treatment of the outer surface of the pivots in order to make it more suitable to withstand the wear of the rolling bodies.
This treatment is currently performed on pivots which are separate from the spider and are therefore fixed to the flange of the spider after the treatment has been completed.
Accordingly, although this solution allows for stronger pivots, it requires a more complicated and expensive process and necessarily entails operations for fitting the pivots to the flange. This results in additional burdens in terms of materials and machining, such as the provision of seating holes in the spider flange, threaded tangs on the pivots which are adapted to be inserted in the seating holes of the flange and are fixed by nuts and washers, and treatments for finishing the various parts.
The object of the present invention is to obviate the above-cited drawbacks of conventional devices, i.e., to provide a monolithic spider for an epicyclic reduction unit which allows to obtain a structure which is simple and has a minimum number of parts that are subject to wear.
The present invention achieves the above object with a structure which is simple, relatively easy to provide in practice, safe in use, effective in operation and has a relatively low cost.
These and other objects and advantages of the present invention will become apparent hereinafter and are achieved by the spider for an epicyclic reduction unit according to the present invention. The present invention is provided with planetary gear supporting pivots which protrude from a flange, wherein the pivots are monolithic, or integral with the flange and have a surface for the rolling of rolling bodies of bearings for supporting planetary gears having a high level of hardness achieved by a thermal treatment for surface hardening.